1. Technical Field
This disclosure relates to an electromechanical transducer, a droplet ejection head, and a method for manufacturing the electromechanical transducer, and more specifically to an electromechanical transducer including an electromechanical transducer film, a droplet ejection head incorporating the electromechanical transducer, and a method for manufacturing the electromechanical transducer.
2. Description of the Related Art
Related-art image forming apparatuses, such as copiers, facsimile machines, printers, or multifunction printers having two or more of copying, printing, scanning, facsimile, plotter, and other functions, typically form an image on a recording medium according to image data by an inkjet method using ink.
For example, such image forming apparatuses may include a droplet ejection apparatus incorporating a droplet ejection head that ejects ink droplets onto a recording medium to form an image on the recording medium. The droplet ejection head includes a nozzle that ejects droplets, a pressure chamber in communication with the nozzle, and a pressure generator that presses against liquid contained in the pressure chamber. The pressure generator includes a piezoelectric, electromechanical transducer, having an electromechanical transducer film made of a piezoelectric substance, mounted on a diaphragm constituting a part of a wall of the pressure chamber. The piezoelectric, electromechanical transducer employs a longitudinal oscillation mode (e.g., a push mode) or a transverse oscillation mode. The longitudinal oscillation mode uses compression and expansion of the electromechanical transducer film in a thickness direction thereof, that is, a direction of an electric field. The transverse oscillation mode uses compression and expansion of the electromechanical transducer film in a direction orthogonal to the thickness direction thereof. Since the entire electromechanical transducer film vibrates as if it bends in the transverse oscillation mode, the transverse oscillation mode is also called a flexural oscillation mode or a bend mode. As the electromechanical transducer deforms in those oscillation modes, the diaphragm mounting the electromechanical transducer is displaced and pressed against liquid inside the pressure chamber.
The piezoelectric substance of the electromechanical transducer film is made of lead zirconate titanate (PZT) having a perovskite crystal structure. The PZT has main crystal planes of a {100} plane, a {110} plane, and a {111} plane. The electromechanical transducer film made of the PZT uses the {100} plane and the {111} plane mainly among the three main crystal planes, that are oriented to be orthogonal to the thickness direction of the electromechanical transducer film, thus producing a PZT film.
For example, JP-2003-188431-A and JP-2004-104066-A disclose the PZT film in which a (100) plane is oriented to be orthogonal to the thickness direction of the electromechanical transducer film. JP-2008-192868-A discloses a piezoelectric substance film that has a crystalline orientation in which the (100) plane is orthogonal to the thickness direction of the piezoelectric substance film and a full width at half maximum, that is, a half peak width, not smaller than 3 degrees in an X-ray diffraction rocking curve method.
The electromechanical transducer including the piezoelectric substance film in which the {100} plane is orthogonal to the thickness direction of the film deforms in a substantial amount when it is applied with voltage during an early stage after manufacturing. However, the amount of deformation of the electromechanical transducer may degrade over time. For example, when a driving voltage for driving the electromechanical transducer is applied to the electromechanical transducer repeatedly, the electromechanical transducer may deform in a decreased amount over time as it is applied with a predetermined driving voltage. As the amount of deformation of the electromechanical transducer decreases, the electromechanical transducer may displace the diaphragm insufficiently and therefore the diaphragm may press against liquid in the pressure chamber insufficiently.